1. Field of the Invention
The invention relates to a piezoelectric resonator and a manufacturing method thereof, and more particularly to a piezoelectric resonator with a built-in capacitor load.
2. Description of the Related Art
A quartz crystal is a piezoelectric component, which outputs a resonant frequency with high precision when a voltage is applied thereto.
FIG. 1 shows an equivalent circuit of a quartz crystal 900, which includes an equivalent resistor R1, an equivalent capacitor C1, and an equivalent inductor L1 connected in series, and a capacitor C0 connected in parallel. The resonant frequency of the quartz crystal 900 is determined by a resistance of the equivalent resistor R1, capacitance of the capacitors C1, C0, and an inductance of the equivalent inductor L1.
FIG. 2 shows a conventional resonator circuit 800 of a piezoelectric transformer applied in an inverter. The conventional resonator circuit 800 includes a quartz crystal 900, two resistors 831 and 832, two amplifiers 811 and 812, and two capacitor loads Cg and Cd. Two terminals of the quartz crystal 900 are respectively coupled to the capacitor loads Cg and Cd, and respectively coupled to the resistors 831 and 832. One terminal of the quartz crystal 900 is further coupled to the amplifier 811. A resonant signal of the resonator circuit 800 is outputted through the amplifier 812.
Referring to FIG. 3, a conventional piezoelectric resonator 9 comprises a ceramic cap 91, a ceramic base 92, a quartz chip 93 disposed between the cap 91 and the base 92, two electrodes 94 respectively disposed on two sides of the quartz chip 93, a conductive silver paste 95, a low temperature glass 96, two vias 98, and two conductors 99.
The ceramic cap 91 is bonded to the ceramic base 92 using the low temperature glass 96, and the electrodes 94 are connected to the conductors 99 on the base 92 through the conductive silver paste 95, a circuit (not shown), and the vias 98.
However, the equivalent circuit of the piezoelectric resonator shown in FIG. 3 is that shown in FIG. 1, and the resonant frequency is determined by a thickness of the quartz chip 93 without the capacitor loads Cg and Cd shown in FIG. 2. In addition, the conventional piezoelectric resonator 9 comprises many different materials, and results in the following drawbacks:
1. Using the conductive silver paste 95 to connect the electrodes 94 to the circuit and the conductors 99 can cause release of a solvent gas, and leads to an aging (frequency shift) issue.
2. Physical properties (such as expansion coefficient) differ among different materials, and may result in instability of the resonant frequency of the piezoelectric resonator 9.
3. Seam welding or low temperature glass bonding produces stress on the ceramic base 92 and the quartz chip 93, and may result in product deterioration.